Mechanical sighting devices, which are distinguished from optical or image-forming sighting devices, generally include a combination of front and rear sights spaced along a length of a barrel. The front sight is typically located at the forend of the barrel in a position that protrudes above the muzzle of the barrel, and the rear sight is located between the front sight and the eye of a shooter. Aim is taken by aligning a top of the front sight and a target with a centering feature, such as a peep or notch, in the rear sight.
Once installed and properly aligned, the sights are generally fixed. However, adjustments can be made by loosening or partially disassembling components and resetting the components in new positions or by adding or replacing components to make more significant adjustments. Some sights, particularly rear sights, incorporate adjustment mechanisms to make changes in elevation or windage. Sight verniers are sometimes used to scale the adjustments.